Recent emissions regulations of each country include more stringent provisions on particulate matter (PM) included in automotive exhaust gas. In particular, while cylinder injection internal combustion engines have an advantage of high output and low fuel consumption over intake-port injection internal combustion engines, the cylinder injection internal combustion engines are disadvantageous in that fuel with large particle sizes adheres to and stays on a piston crown surface and a cylinder bore wall surface and that mixing of fuel and air tends to suffer nonuniformity, leading to a propensity to generate PM.
Existing PM reduction measures for such cylinder injection internal combustion engines include the use of a dual internal combustion engine that includes a cylinder-injecting injector and an intake-port-injecting injector attached on an identical cylinder to allow the use of the intake-port-injecting injector for a travel region with significant PM generation in order to reduce PM. The measures also include the use of a filter attached to capture PM. While these measures are expected to be highly effective at reducing PM, they suffer increased costs due to the addition of new devices.
Approaches to the reduction of PM without adding new devices are, thus, sought after, and one such approach is a technique disclosed in PTL 1 for multiple injection control to perform multiple fuel injections in one cycle. Through this control, the amount of fuel adherence in the cylinder can be reduced and the uniformity of air-fuel mixture can be improved, leading to reduction in PM.
This multiple injection control, however, increases the number of injections without changing the fuel injection quantity, and thus the fuel injection quantity for one injection is smaller than a traditional fuel injection quantity. Such a smaller fuel injection quantity requires improved accuracy of lower fuel flow rates, which have been rarely used traditionally, leading to cost increase for the improvement of injector accuracy.
As a solution to this problem, control techniques described in PTL 2 and PTL 3 can be used. The technique in PTL 2 is to detect valve opening/closing timings of an injector from an injector drive current displacement point for feedback to injector power distribution time control. The technique in PTL 3 is to detect valve opening/closing timings of an injector from a piezoelectric element for feedback to injector power distribution time control.
Through the control techniques in PTL 2 and PTL 3, the valve opening/closing timings of the injector can be detected by using an existing sensor for feedback to the power distribution time control, thereby curbing the cost increase for the injector, achieving the fuel injection with high accuracy, and reducing PM in an inexpensive manner.